Kidney function and all-cause mortality in the oldest-old population: a three-cohort longitudinal study.

Area of Science:

• Gerontology and Geriatric Medicine
• Nephrology
• Epidemiology

Background:

• Global life expectancy is increasing, necessitating a clearer understanding of kidney function's prognostic value in the oldest populations.
• Conventional estimated glomerular filtration rate (eGFR) thresholds for chronic kidney disease (CKD) may not be appropriate for centenarians and supercentenarians.
• Age-adapted definitions of kidney function are needed to accurately assess health risks in extreme longevity.

Purpose of the Study:

• To investigate the association between kidney function and all-cause mortality across different age groups, focusing on the very old.
• To determine if current eGFR thresholds for CKD accurately predict mortality in centenarians and supercentenarians.
• To establish age-specific prognostic thresholds for eGFR in individuals aged 85 and older.

Main Methods:

• Analysis of data from the Tokyo Centenarian Study, Japan Semi-supercentenarian Study, and Kawasaki Ageing and Wellbeing Project, including 1,918 participants with baseline serum creatinine.
• Calculation of eGFR using both creatinine and cystatin C, following the Japanese Society of Nephrology equation.
• Assessment of mortality associations using Cox regression models and estimation of standardized 3-year absolute risks.

Main Results:

• Lower cystatin C-based eGFR was consistently linked to higher all-cause mortality, while creatinine-based eGFR showed weaker associations.
• Prognostic eGFR thresholds decreased with age: approximately 45 mL/min/1.73 m² for ages 85-89, 30 mL/min/1.73 m² for ages 100-104, and 15 mL/min/1.73 m² for ages ≥105.
• The absolute risk difference in mortality between low and high eGFR groups varied by age, being modest in younger-old adults, larger in centenarians, and attenuated in supercentenarians.

Conclusions:

• Estimated glomerular filtration rate remains a relevant prognostic marker for mortality even in advanced age.
• The prognostic significance and absolute risk differences associated with eGFR vary considerably across extreme age groups.
• Adoption of age-specific CKD thresholds is supported to improve prognostic accuracy in centenarians and supercentenarians.